1. I don't know who to say.
2. I don't know who to say about.
3. I don't know who I should say to.
4. I don't know who should say.
5. I don't know whom to say.
6. i don't know whom to say about.
(Which expressions are right?)

First, Lidya, if you have a question, it is much better to put it in as a separate post in <Post a New Question> rather than attaching it to a previous question, where it is more likely to be overlooked.

As far as I know, Robin hood is a folklore hero rather than a real person. However, since this is not my area of expertise, I searched Google under the key words "Robin Hood birth" to get these possible sources: